1. Field of the Invention
The present invention relates to a refrigerator temperature control system in which a compressor for compressing a refrigerant, an evaporator fan for moving air about an evaporator and a condenser fan for moving air about a condenser are driven at variable speeds for controlling the temperatures of a freezer compartment and a fresh food compartment.
2. Description of the Prior Art
In a refrigerator having a freezer compartment and a fresh food compartment, the temperature of the respective freezer and fresh food compartments, gradually rise due to heat transfer through the walls and door of the refrigerator as well as from the frequent opening of the door or doors of these compartments and loading therein of foods or the like. Various methods for controlling the temperature of the respective freezer and fresh food compartments are known.
Typically, a refrigerator may include a refrigeration system having a compressor motor, an evaporator fan motor and a condenser fan motor which cycle on together in response to higher than desired temperatures in the freezer compartment and cycle off together when the desired temperature in the freezer compartment is achieved. The temperature within the fresh food compartment is typically controlled by a baffle disposed within an air duct for providing air control means for varying the recirculation of air within the refrigerator between the freezer compartment and the fresh food compartment.
Another known method of controlling the temperatures within the respective freezer compartments and fresh food compartments are disclosed by R. E. Tobey in U.S. Pat. No. 3,015,215. Tobey discloses using a two speed continuously operating evaporator fan motor for controlling the temperature of the fresh food compartment. When the fresh food compartment is at or below a desired temperature, the evaporator fan motor operates at a low speed to circulate an air stream from the freezer compartment to the fresh food compartment. When the fresh food compartment is above the desired temperature, the evaporator fan motor operates at a high speed to increase air circulation between the freezer compartment and the fresh food compartment. A single speed compressor motor and condenser fan motor is independently cycled on and off to maintain the freezer compartment at the desired temperature.
F. L. Stevens, in U.S. Pat. No. 3,359,751, discloses a method for controlling a two temperature refrigerator using two separate evaporator fans in a side-by-side refrigerator application. The Stevens patent discloses a system having a compressor motor and condenser fan motor and a first evaporator fan which are cycled on and off together for controlling the freezer compartment temperature. A second evaporator fan is cycled on and off for controlling the fresh food compartment.
All of the above described refrigeration control methods utilize cycling on and off a compressor motor, an evaporator fan motor and a condenser fan motor for temperature control. This cycling in an on-off manner of the compressor motor, evaporator fan and condenser fan must occur quite often to keep the respective temperatures of the freezer and fresh food compartments within desired ranges. However, frequent starting and stopping tends to decrease the operating life of the system. Each start up of a motor causes relatively high currents to be fed to the motor windings, thereby causing heating of the electrical power driving components and the motor itself, and also causes power losses within the motor windings. Further, it is believed that an energy loss of as much as 10-15% may occur when a compressor is cycled on and off at particular cycle rates. This significant energy loss is believed to be due to the migration of liquid refrigerant to ineffective cooling locations within the refrigeration system. For example, liquid refrigerant may migrate, during the off condition of the compressor, to locations beyond the evaporator, and upon subsequent restart of the compressor, the liquid refrigerant vaporizes outside the evaporator where no cooling effect is acquired as a result of such vaporization.
The above described undesirable results of cycling the compressor motor, evaporator fan motor and condenser fan motor may be overcome by utilizing variable speed motors. Erdman, in U.S. Pat. No. 4,459,519, disclosed an arrangement for utilizing a variable speed compressor motor and evaporator fan motor for controlling the temperature of a single temperature refrigerator. Erdman discloses varying the evaporator fan speed for controlling the temperature of the single compartment temperature. Feedback from the fan speed controls the desired temperature setting of the evaporator and the compressor motor speed is varied to achieve the desired temperature setting of the evaporator.
Therefore, it would be desirable to develop an improved control arrangement for controlling the temperatures within a refrigerator having a freezer compartment and a fresh food compartment in which the control arrangement utilizes variable speed motors for achieving the above stated beneficial effect. Further, it would be desirable to develop an improved control arrangement for controlling the temperatures within a refrigerator having a freezer compartment and a fresh food compartment and which utilizes variable speed motors and wherein the refrigerator does not require a separate movable baffle arrangement for controlling air recirculation from the freezer compartment to the fresh food compartment.